Controlling droplet size in emulsions using on-line particle size analysis

The Insitec L represents a breakthrough for manufacturers wishing to monitor and control the homogenization process. This real time data can be used as an aid in product development and as a process control & optimization tool.


Emulsions are quite common in the food, dairy, cosmetic and pharmaceutical industries. Typical examples range from yoghurts and salad dressings, to topical ointments and moisturizers. In most cases an emulsion is produced using a Homogenizer, which uses pressure to control particle or droplet size.

Droplet size affects a product's taste, consistency, performance and stability. For this reason manufacturers closely monitor droplet size to ensure product quality.

In the past, particle size analysis was always performed in the laboratory, using periodic sampling and small, potentially unrepresentative, sample volumes. This was a perfectly suitable procedure from a quality control perspective, but it was insufficient to make a genuine contribution to real process understanding or the automation of process control.

For several years Malvern Process Systems has been supplying the Insitec L on-line particle size analyzer, which makes continuous measurements on large sample volumes directly on the process line and in real-time. The Insitec has brought a new dimension to optimization, with the capability to provide fully automated control and monitoring of the manufacturing process.


The Insitec is a laser diffraction based instrument that continuously monitors the scattering of light from particles passing through the measurement zone.

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Using the rigorous Mie Light Scattering Theory, this diffraction of light is measured and the resulting particle size distribution is calculated.

In a typical emulsion system, material passes through a liquid flow cell where the measurement is made as shown in the diagram below. Since material continuously passes through the measurement zone, a particle size distribution is generated as a function of time.

RTSizer is Malvern's proprietary, Windows based software which presents this data in a user friendly format. Typical process control parameters such as the average particle size, Dv(90), %<, and mesh can be trended as a function of time.

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Malvern Link is a Malvern supplied software package that can export data to the plant for archiving and process control.

The Malvern OPC server provides an interface between RTSizer and the process plants OPC client. Malvern OPC server for RTSizer is OPC-compliant as dictated by the OPC foundation.


The Data attained compares closely to traditional off-line analysis as laboratory systems are based on the same laser diffraction principle.

The Insitec has the distinct advantage of being right at the process line where the material is in its natural state and particles are less prone to coalesce or agglomerate.

Because the Insitec is continuously monitoring material at the outlet of the Homogenizer, shifts in the particle size can be observed immediately.

One exercise involved varying Homogenizer conditions, monitoring the affects and then optimizing the Homogenizer settings based on the droplet size information gleaned from this exercise. This may be done at the R & D or product development stages or during the start up of the production process. In this case, the Insitec is the key to monitoring the cause and affect of process changes with respect to droplet size.

Depicted on the right is a screenshot of the Insitec software, monitoring droplet size, of material produced by an APV Homogenizer run at various pressures.

The concentration of droplets inside the homogenizer is extremely high and cannot been measured at this concentration by laser diffraction without dilution. For this reason, the Insitec team created an innovative Process Interface Solution (cascade diluter) to tackle the problem of sample dilution in real-time without any sub-sampling bias. This diluter comprises a series of co-axial venturis, each one providing a dilution ratio of 5:1. The higher the concentration, the greater the number of stages used. All stages are tri-clamped together and the device is self-cleaning. This simple but highly effective device (currently being patented) extracts sample from the process, dilutes and transports it to the Insitec flow-cell in a matter of seconds where it is measured in real-time. The screenshot below shows the real-time data collected over the test period.

It is apparent from the trend line that there were 4 different conditions run during this test. Look at the Dv(50) average particle size ( blue line ) and a noticeable shift in droplet size is seen at each of the 4 pressures used during this process test. What is remarkable is that this test was performed and the data for the entire run including all 4 conditions was collected in only 20 minutes. If this test was to be performed in a traditional manner, the operators would have to take samples intermittently during the run and perform the analysis in the lab after the test was complete - an operation typically lasting several hours.

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The Insitec L represents a breakthrough for manufacturers wishing to monitor and control the homogenization process. This real time data can be used as an aid in product development and as a process control & optimization tool in addition to ensuring quality control in production.

The following is a list of key benefits realized by the use of on-line particle size analysis:

  • Reduction of Start-up times
  • Detection of process perturbations
  • Maximization of throughput
  • Observation of the effects of process changes
  • Reduction of off-spec material produced
  • Reduced operator sample time


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